The use of communication systems through which to communicate is pervasive throughout modern society. And, the need to have access to a modern communication system through which to communicate is therefore a common requirement for many. Various different types of communication systems have been developed and have been deployed through which to communicate data to effectuate varied types of communication services.
A communication system is formed, at a minimum, of a sending station and a receiving station, interconnected together by way of a communication channel. Data that is to be communicated to effectuate a communication service through operation of a communication system is sourced at, or is otherwise provided to, the sending station. The sending station converts, if necessary, the data into a form to permit its communication upon the communication channel and causes the data to be communicated thereon. The receiving station operates to detect the data communicated upon the communication channel and delivered to the receiving station and to operate upon the data once received thereat to recover the informational content thereof.
A telephonic communication system is an exemplary type of communication system. Usage of a telephonic communication system through which to communicate telephonically is pervasive. And, telephonic communication systems have been deployed, now to encompass a significant portion of the populated areas of the world. Generally, a telephonic communication system provides for the communication of both voice data and non-voice data. Two-way, full duplex communication of the data is usually provided by a telephonic communication system.
Users communicate by way of a telephonic communication system by way of communication stations referred to as telephonic stations. A telephonic station at which a call is initiated is referred to as a calling station or calling party. And, a telephonic station to which a call is placed is referred to as a called station or called party.
A radio telephonic communication system, such as a cellular communication system, also provides for telephonic communication of voice and non-voice data. The data is communicated by way of channels defined upon a radio air interface, obviating the conventional requirement that the telephonic stations be fixedly connected to wireline connections to permit the communication of data to effectuate a communication service. Because the need for the wireline connection is obviated, user mobility during communication operations is enhanced.
Additionally, telephonic stations, typically referred to as mobile stations, used in a radio telephonic communication system, are typically of dimensions permitting their carriage by a user. The use of radio links, and radio channels defined thereon, together with the ease of carriage of the mobile stations, permits the user of a mobile station to communicate telephonically from, and between, locations at which telephonic communications had previously not been feasible.
Conventional, wireline telephonic stations are sometimes adapted to include, or to permit the connection thereto, of data text devices, such as TTY devices. TTY devices permit telephonic communications to be effectuated by, e.g., hearing-impaired users. A hearing-impaired user is generally less able, or unable, to hear voice data delivered to a telephonic station and, sometimes, is unable adequately orally to communicate voice information. To compensate for this impairment, a user enters data that is to be communicated by way of the TTY device, and a recipient of the data receives the transmitted data in textual form.
The TTY devices were developed initially for their use in wireline telephonic systems. Their adaptation for use in radio telephonic communication systems is non-ideal, particularly when the radio telephonic communication system forms a digital communication system. A primary reason for this is that digital radio telephonic communication systems regularly utilize speech coding techniques to encode data prior to its communication upon radio channels defined upon a radio air interface. Speech coders are generally optimized to encode speech-like signals, not textual data. And, transmission errors during communication upon non-ideal communication channels are sometimes also more problematical when textual data rather than speech data is communicated. Modulation techniques, and modems that carry out such modulation techniques, conventionally utilized by TTY devices were not developed to take into account coding performed by speech coders to which a TTY device, and the TTY data generated thereat, passes when connected theretogether.
A CTM (Cellular Text Telephone Modem) scheme has been proposed that provides an improved manner by which to communicate text data. And, radio telephonic communication system apparatus, both for the infrastructure part of the system and for a mobile station operable therein, is being developed to facilitate the communication of CTM-modulated data.
Schemes are set forth by which to provide TTY modulation at an external TTY device that is connected to a radiotelephonic station, herein referred to as a mobile node, in the event that CTM modulation can not be performed. But, mobile nodes are now constructed to include internal TTY devices, or applications. And, the text data formed at the internal device is applied directly to a CTM modulator of the mobile node. If a connection is able to be formed to communicate the text data, to form CTM-modulated data, the data is communicated.
The existing scheme, however, generally fails to provide a manner by which to communicate the internally-sourced textual data in the event that a connection is unable to be formed to communicate the CTM-modulated textual data. In the event that such a connection is unable to be formed, presently, there is generally no standard procedure by which to ensure that the textual data is communicated.
The inability of a user to communicate the internally-sourced textual data is particularly problematic when the data is to be communicated pursuant to a request for emergency assistance, such as, in the United States and Canada, an emergency 911 call. A fallback technique by which to communicate the internally-sourced textual data in the event that CTM-modulated textual data cannot be communicated would, therefore, be advantageous.
It is in light of this background information related to the communication of textual data in a radio communication system that the significant improvements of the present invention have evolved.